The broad objective of the proposed research is the elucidation of the ultrasonic communication system in the reproductive behavior of rats. The research is focused on three main areas: (1) the occurrence and characterization of ultrasonic vocalizations that normally are produced during reproductive activity; (2) the communicative functions of these vocalizations; and (3) the physical properties of the ultrasonic message. Research in the first area will involve observation of mating in rats when one of the participants is devocalized, such that the ultrasonic contribution of both the male and female can be detected and then recorded for sonographic analysis. The communicative functions of the ultrasonic vocalizations will be determined by using muted rats and observing behavioral and physiological events in rat reproduction whih result as a consequence ofthe presence or the absence of tape recorded ultrasonic vocalizations. In the third area of research (a) ultrasonic vocalizations will be examined by fast Fourier transform analylsis, (b) critical acoustic features will be determined by testing muted rats in the presence of synthetic ultrasonic signals, (c) the influence of contextual cues will be investigated, and (d) the cpapcity of rats to utilize complex ultrasonic information will be ascertained. This proposed research will use psychobiologcal and acoustical techniques to broaden our knowledge of rat reproductive behavior and physiology and thus increase the usefulness of the rat as a model for behavioral, physiological, and biomedical research.